With the demonstration that up to 80% of Rett syndrome cases are caused by mutation in a methyl DNA-binding protein, MeCP2, the analysis of neurological effects and mental retardation in this disease must focus on associated changes in chromatin. The working hypothesis is that chromatin remodeling based on methylation must be modified to turn on or off critical proteins active in brain function. Almost certainly, a multiprotein complex containing MeCP2 is involved, for it is becoming increasingly clear that chromatin remodeling like many reactions in the cell nucleus is carried out by such complexes. Often, one protein can be part of several complexes, with each complex having a unique function. In fact, MeCP2 has been shown to co-fractionate and coimmunoprecipitate with histone deacetylase HDAC1 and transcription corepressor mSin3A, proteins that are presumably part of the complex. However, the entire complex (or complexes) containing MeCP2 has not been completely purified or characterized. We want to apply purification procedures that we have developed and successfully used to analyze other disease-related chromatin remodeling complexes to identify the protein partners of MeCP2 in the cell. The proximal goal of this research is to understand the function of MeCP2 in vivo. So far we are trying to make good antibodies against MeCP2. We are also in the process of establishing cell lines that stably expressed epitope-tagged MeCP2. Hopefully, these strategies will allow us to purify the physiological MeCP2 complex.